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Notes from booklet Flashcards

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1
Q

Mass number is what

A

protons and neutrons

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2
Q

Atomic number is

A

protons

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3
Q

Tungstan has a K shell energy of what?

A

69.5keV

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4
Q

What are properties of isotopes

A

same chemical properties as same protons

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5
Q

How does Iodine 123 decay?

A

by 160keV Gamma Ray

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6
Q

Isotope vs isotone?

A

Isotope has same number of protons. Isotone same number of neutrons.

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7
Q

what is a bacquerel?

A

Number of decays per second

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8
Q

What is emitted with a beta plus decay?

A

A positron

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9
Q

when a positron and electonr anihilate what is the energy of the resulting photons?

A

511kEV each

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10
Q

What is emitted in beta minus decay?

A

electron

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11
Q

EM waves travel in what way?

A

perpendicular to direction of travel and 90 degrees to each other

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12
Q

what is plancks constant?

A

the constant connecting Energy and frequency.

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13
Q

relationship of frequency and wavelength

A

f = 1/ wavelength

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14
Q

equation for contrast

A

propotional to (u1 - u2) x thickness of material

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15
Q

in CT a reduced FOV and increased matrix size causes what for the noise

A

smaller pixels, therefore reduced SNR.

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16
Q

in a single slice scanner - does pitch affect the noise?

A

no, only the spatial resolution due to partial voluming.

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17
Q

in a multislice scanner does pitch incease noise

A

yes

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18
Q

relationship of SNR and slice width

A

SNR is proportional to the square root of slice width.

to doulbe your SNR you have to quadruple the slice width.

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19
Q

relationship of SNR and mA

A

SNR is proportional to the square root of mA

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20
Q

How does windowing affect noise

A

Decreasing the windowing will increase noise. However the SNR is still the same.

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21
Q

What type of noise is the most significant

A

Quantum, electronic the least

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22
Q

CT - cupping is the effect of what?

A

Beam hardening

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23
Q

Ring artefacts are less suceptible in multi or single slice

A

In multi

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24
Q

XR source to patient distance will affect what

A

spatial resolution

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25
Q

CTDI depends on what?

A

mA, kV and filtering.

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26
Q

DLP is what?

A

CTDI (vol) xL

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27
Q

effective dose and DLP relationship

A

E = DLP multiplied by the constant for body region and scanner design.

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28
Q

in fluoro - scatter of light in the output window will affect what>

A

contrast

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29
Q

in fluoro - a single photon will cause how many electrons to be stimulated in the photocathode?

A
  1. II input window

Convex metal shield that covers the input face of the II
Usually made of aluminium or titanium foil (low Z metal) to allow x-ray beam to enter with minimum attenuation
Provides protection for sensitive input components of the tube and maintains the vacuum

  1. Input phosphor

Layer of sodium activated caesium iodide (CsI:Na) for good x-ray absorption efficiency (70-90%)
Channelled into tiny needle-like crystals (5µm in diameter) with fibreoptic-like characteristics
Deposited on a thin aluminium substrate
CsI:Na usually 400-500µm thick
Each x-ray photon produces ~3000 light photons in the blue spectrum

  1. Photocathode

Fluorescent emission from phosphor then absorbed in a light-activated photocathode comprising a very thin layer of antimony caesium (SbCs3) alloy that has a spectral sensitivity well matched to the blue light emission of CsI:Na
Absorption of the fluorescent light photons releases a pattern of electrons in the body of the II tube
Approximately 200 electrons released per absorbed x-ray photon

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30
Q

what is DQE?

A

out brightness squared / input signal squared

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31
Q

fluoro - what happens to DAP on magnification

A

DAP will decrease.

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32
Q

Grid controlled tubes are used in what kind of fluoro

A

Pulsed mode

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33
Q

in mammography what kind of focal spot size is used

A

smaller

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34
Q

as the tissue thicness changes in fluoro what happens to the dose rate?

A

It will stay the same as kV and mA are changed to keep output the same.

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35
Q

in fluoro: what is the quation for minification?

A

input diameter squared /output diameter squared

Minification gain = (Dinput / Doutput)2 (where D is diameter of input and output screen respectively)

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36
Q

Brightness gain =

A

minification x flux gain

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37
Q

in fluoro for kids what type of kV do we use?

A

High kV –> but the resulting image is poorer.

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38
Q

in fluoro - good bone to soft tissue is achieved with high or low kV

A

low kV

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39
Q

what is the benefit of compression?

A

it reduces gemoetrical and movement unsharpness

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40
Q

decreased electrons at the edges of the edges of the fluoro II causes increased

A

distrotion and decreased brightness

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41
Q

in ct: Beam p =

A

movement / collimation

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42
Q

in Ct: slice p =

A

movement /slice width

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43
Q

relationship between collimation and slice width

A

collimation is greater than or equal to slice width.

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44
Q

relationship between slice p and beam pitch. (in ct)

A

slice p greater than or equal to beam pitch.

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45
Q

in ct what is the spatial resolution

A

1 / (2 x pixel size)

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46
Q

in ct - what is the pixel size

A

FOV / matrix

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47
Q

which body is contacted if a high dose is given to a patient

A

CQC

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48
Q

List some gamma emitters

A

Tc99m
I 123
Ga 67
In 111

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49
Q

In a fission reactor Uranium becomes what?

A

Mo99.

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50
Q

in NM imaging - what happens to the image if the collimator has wider holes?

A

sensitivity goes up

resolution goes down

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51
Q

In NM imaging when is high sensitivity particularly good?

A

When short frame rate is needed for dynamic studies.

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52
Q

why do we not use a collimator in in PET?

A

want to increase the sensitivity

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53
Q

T2 is loss of net WHAT magnetisation

A

transverse

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54
Q

in MRI: relationship between Lamor frequencyt and T

A

they are proportional. Ie At 1.5T the L is 64 MHz and increases with increasing T.

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55
Q

in MRI - why do lesions have a longer relaxation time

A

they have a greater content of just water than most tissues.
So a longer T1.

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56
Q

Describe the relationship of T1 loss of magnetisation

A

Spin lattice - loss to external molecules.
Pure liquid - lots of movement, no time to interact so LONG relaxation
Viscous - less rapid movement, time to interact. Short relaxation.

Solids - the molecules are fixed so can’t interact. Therefore T1 is LONG again .

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57
Q

Describe the T2 loss of coherance

A

T2, spin spin, loss to each other.
They affect each other - lose coherance.
In liquids - move freely, magnetic field evens out. T2 is long. LONG T2
In solids - can’t move, field is fixed so affects it. Dephase quickly. SHORT T2.

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58
Q

WHich is shorter T2 or T1

A

T2 is always shorter than T1.

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59
Q

What affect does the Tesla field strength have on T1 and T2

A

T2 is unaffected (transverse)

T1 timings increase.

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60
Q

US: how long are wavelengths normally

A

0.1 - 1.5mm

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61
Q

Abdo US frequency

A

3.5 to 5MHz

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62
Q

How much is reflected from a muslce /bone interface

A

40%

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63
Q

What is the equation for impedance?

A

Velocity x density

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64
Q

What is the units of impedance

A

kg/m-2/s

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65
Q

What are the units of intensity?

A

W / mm2

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66
Q

What is inensity proportional to?

A

amplitude squared

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67
Q

resonant frequency is what relation to PZT?

A

twice the thickness

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68
Q

Damping causes what?

A

decrease in amplitude

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69
Q

High damping causes what?

A

decreased amplitude but a wider band of frequencies and a short pulse.

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70
Q

Low damping

A

higher amplitude, longer pulse.

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71
Q

High Q is which damping - high or low

A

low

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72
Q

continuous mode has what kind of frequency?

A

single frequency

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73
Q

pulsed mode is what kind of frequency?

A

range of frequencies

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74
Q

near field equation is

A

radius squared / wavelength.

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75
Q

what does the impednace matching layer do

A

provides further damping in addition to achieving max energy transfer

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76
Q

for a fixed transduceer radius how does the near field change if the frequency is decreased?

A

decreased.

due to Near field = r squared / wavelength

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77
Q

beam width =

A

focal length x wavelength

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78
Q

axial resolution =

A

half the spatial pulse length

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79
Q

lateral resolution =

A

ultrasound beam width.

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80
Q

which is better - axial or lateral resolution?

A

axial resolution is better

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81
Q

how does diamter of transducer affect the resolution in the near field

A

if its a smaller diameter it will be a better resolution in the near field.

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82
Q

What things can change the lateral resolution?

A

frequency, focusing, transducer diamter, distance from the transducer.

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83
Q

Doppler shift frequency is proportional to

A

cosine angle of US

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84
Q

what is the maximum doppler shift frequency that can be detected?

A

PRF / 2

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85
Q

what can a high PRF create?

A

range ambiguity as echoes are generated generated deeper will be registered as being more superficial.

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86
Q

speed is = to what (relationship of rigidity and density)

A

= square root of (k/p)

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87
Q

time is

A

2d / c

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88
Q

Us is what kind of wave?

A

Longitudinal

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89
Q

How fast are waves?

A

1540cm/s

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90
Q

the matching layer serves what purpose?

A

More is transmitted, less is reflected

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91
Q

What is Rayleigh scattering?

A

When particles are smaller than the size of the wavelength grainy

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92
Q

what is compound imaging?

A

look behind structures. good fro aorta

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93
Q

What is harmonic imaging?

A

Non linear propogation of waves to increase resolution

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94
Q

what kind of frequency does the harmonic imaging use?

A

Higher frequency

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95
Q

Three types of doppler?

A

Continuous, pusled and colour doppler

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96
Q

Does continous doppler offer depth?

A

No

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97
Q

Pulsed wave offers what

A

Depth but lots of alisaing.

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98
Q

What does A, B and M modes mean

A

A for amplitude - depth of boundaries.
B
M - motion of structures like heart valves.

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99
Q

What temperature rise a risk to the foetus?

A

1.5 rise

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100
Q

Which is higher energy the pulsed doppler or B mode?

A

Pulsed doppler

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101
Q

Near field is proportional to what of D

A

D squared

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102
Q

Lateral resolution is best where? and why?

A

in the focal zone due to beam narrowing.

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103
Q

pulse length =

A

number of cycles x wavelength

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104
Q

Q factor equation =

A

F / bandwith

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105
Q

Intensity reflected =

A

Z2 - Z1 / Z2 plus Z1 all squared

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106
Q

F doppler

A

= 2 Ft v cos angle / speed

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107
Q

backscatter is Frequency…..

A

dependant

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108
Q

doppler is best at what angle

A

less than 60 degrees due to cosine

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109
Q

does continuous doppler have a velocity limit

A

no

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110
Q

does pulsed dopper have a velocity limit

A

yes

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111
Q

what value of MI can cause damage?

A

> 0.3

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112
Q

What values are disoplayed for MI and TI

A

if MI greater than 1

if TI is greater than 0.4

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113
Q

In basic sciences - valence band gives what properties

A

the chemical properties, thermal, optical and electrical properties

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114
Q

what is the speed of EM waves in a vacuum

A

travels at speed of light

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115
Q

what kind of radiation do you get in Internal conversion?

A

characteristic radiation as the electrons get replaced.

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116
Q

List some crystals that are used

A

Silver bromide
Sodium iodide
Caesium iodide

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117
Q

What is a coulomb

A

1 a / s

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118
Q

what is an eV

A

it is the energy required to move an electron through one volt.

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119
Q

What happens to the binding energy as the Z increases?

A

the binding energy increases

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120
Q

how does quantum radiation travel

A

in a straight line as packets of ernegy

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121
Q

how does the wave aspect of radiation travel

A

in a transverse waves, sinusoidally varying.

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122
Q

In electromagnetic radiation - travel at…

A

right angles to each other and the direction of travel.

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123
Q

how does the constant, wavelength and frequency are linked

A

constant = wavelength x frequency

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124
Q

what is photon fluence?

A

amount of photons that pass through an area in space multiplied by all their energies

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125
Q

what is energy fluence rate?

A

it is the photon fluence / second

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126
Q

air kerma

A

air kerma is measured as a substitute for photon fluence.

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127
Q

equation of air kerma and distance

A

air kerma B / air kerma point A = distance of A squared / distance of b squared

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128
Q

How do the electrons in the tube lose their energy

A

Multiple little enrgy losses - heat

large ernegy losses with inner shell or the nucleus.

129
Q

Why does the energy of the electron need to be greater for higher atomic numbers

What affect does this have on the emitted photons

A

The nuclear force holding the K shell electron is stronger.

The photons after this interaction are therefore of a higher energy.

130
Q

Does tube voltage affect the photons emitted from charachteristic interactions?

A

It does in order for the electron energy to be over the K binding energy. However the energy of the photons will be changed based on the atomic number.

131
Q

Intensity of the brehmstrauling radiation is proportional to

A

KV squared x mA (number of electrons)

132
Q

efficiency of XR production =

A

XR output / electrical power supplied.

133
Q

what is the electrical power supplied =

A

proporitonal to kV x mA

134
Q

Intensity of XR production

A

proportional kV squared x mA

135
Q

interaction of XR with matter - what are the three ways

A

Transmitted (unaffected), absorbed (lose all their eneregy) and scattered

136
Q

what is half value thickness?

A

thickness to reduce by 50%

137
Q

What is the relationship between LAC and HVL

A

LAC = 0.693 / HVL

138
Q

How can you increase the LAC?

A

increase the density or the atomic number

139
Q

Intensity of beam equation

A

I = I E to the pwoer of u d

140
Q

why do we consider LAC with a thin beam?

A

the wide beam will have scatter that will give a false higher reading of radiation

141
Q

Attenutation - low energy or high energy are attenuated more?

A

Low energy are attenuated more

142
Q

Which causes is worse for image quality - high energy or low energy beam?

A

High ernegy - higher energy scatter gets through.

143
Q

What are the types of attenuation?

A

Compton (inelastic)
Phtoelectric - TOTAL absorption
Elastic.

144
Q

In what direction can compton scatter be in?

A

in all direction

145
Q

Compton - what direction will the elctron go in?

A

sideways or forwards (not backwards)

146
Q

probability of compton is proportional to what?

A

proportional to physical density (ie mass and electron density)

147
Q

which has more energy - a forward scattered electron or a side scattered electron?

A

Forward scattered has more

148
Q

relationship of compton scatter to density and energy

A

C = density / E

149
Q

what is the equation for Photoelectric effect

A

PE = density x Zcubed / E cubed

150
Q

describe an absorption edge?

A

as the energy increase the chances of PE decrease, however when it hits a new electron level the chances suddenly jump up as electrons can be hit from this level.

151
Q

Which kind of effect, compton or PE, is affected by Z and energy of the photons?

A

PE is affected most by both.
Compton is NOT related to Z number (only electron density)
PE is more sensitive to energy as it is cubed

152
Q

sift tusses are affected by compton or PE

A

compton

153
Q

heavy stuff is affected by compton or PE

A

PE (lead ect)

154
Q

the ionizing path of secondary radiation (within tissues) is what ratio

A

proprotional to 1 / density

155
Q

when aluminium is used to filter a beam - what interaction is occurring?

A

Low energy photons are taken out by the metal through PE interaction.

156
Q

How much aluminium is used?

A

2.5mm at 70kv

157
Q

at diagnostic energies - absorbed dose and air kerma are

A

the same

158
Q

how can you improve the quality / intensity of the XR beam?

A

INcrease the kv
increase mA

intensity proportional to Ma x kV square / Fsquared

159
Q

which happens quicker phospholuminescence or fluorescence?

A

Fluoro

160
Q

what is the usual angle of the anode?

A

7 - 20 degrees

161
Q

what type of vapour pressure is desirable for the thermionic emission?

A

low

162
Q

high kV will affect scatter how?

A

increase, more scatter closer to the film

163
Q

mass attenuation coefficient is what

A

LAC / density

164
Q

what are the units of mass attenuation?

A

cm squared / g

basically LAC per unit of density

165
Q

why is LAc better than MAC?

A

describes the depth of tissues rather than the mass

166
Q

what is LAC?

A

the fractional reduction in intensity per unit length

167
Q

units of LAC

A

mm -1 (per mm)

168
Q

Total absorption happens in which?

A

Compton or Photoelectric?

169
Q

in XR production - what is inherant filtration?

How much is there?

A

XR passing the tube housing ect

total filter desired is 2.5mm, inherant is 0.5 to 1mm

170
Q

what is the tube rating?

A

a high tube rating means it can lose the heat generated efficiently

171
Q

which type of badge uses a double emulsion film?

A

Film badges

172
Q

Beta radiation can travel

A

a few mm’s

173
Q

Difference between kerma and absoroption

A

Kerma - energy transferred
Absoroption - energy absorbed.
.

174
Q

WHich radiation ionizes directly?

A

XR and photons?

175
Q

LET is what

A

amount of energy transferred in a distance

176
Q

Relative Radiological Efectiveness is what

A

ratio of absorbed doses required to produce the same biological end point for two RADIATION types.

177
Q

Linear no threshold theory exists for which?

A

Stochastic

178
Q

radon decays giving out what

A

Alpha particles

179
Q

Entrance surface dose can be measured with what?

A

TLD

180
Q

Which badge has a linear response over a wide range

A

TLD

181
Q

Which has better sensitivity - film or TLD

A

trick - both the same

182
Q

most precise dosimeters

A

electric ones

183
Q

In MRI the field strength causes what affect on the body

A

PNS from the gradient coils going on and off

184
Q

RF pulse will cause what?

A

Heating

185
Q

Which is shorter T2 or T2*

A

T2*, decays quicker due to inhomogeneities

186
Q

In MRI - what are used to reduce breathing arefacts?

A

Saturation bands

187
Q

frequency encoding is done in how many echoes?

A

one echo

188
Q

should supervised areas have warning signs

A

yes

189
Q

critical examination of installed equipement is usually done by

A

the installer but also the RPA can do this

190
Q

Who should be contacted prior to equipement installation

A

The RPA

191
Q

who chooses the designated areas?

A

RPA

192
Q

Tube leakage from the housing should be what

A

less than 1 mGy/hr @ 1m

193
Q

chance of fatal cancer from 1mSv

A

1 in 20 000

194
Q

As photon energy increases what happens to attenuation

A

it decreases

195
Q

photoelectric effect cause what kind of radiation?

A

characrteristic

196
Q

what kind of interaction is an incident energy completely absorbed

A

photoelectric

197
Q

describe an Auger electron?

A

charachteristic radiation is immediately absorbed in LOW atomic number material. This can result in another photoelectron being ejected. This is an auger electron

198
Q

how does reducing the tube voltage affect side scatter and penetrating scatter?

A

increase side scatter

reduce penetrating scatter

199
Q

probaability of compton effect is proportional to what

A

the density of the material and the electron density

NOT THE ATOMIC NUMBER

200
Q

what is the atomic number of Tungesten and K shell binding energy?

A

74 atomic number

K shell is 70

201
Q

with XR filters, what is the relationship between the peak kV and the absorption edge.

A

The peak kV should be the right (or the high energy side) of the absorption edge.

202
Q

the range of secondary electrons is inversely proportional to what

A

the material density

203
Q

which has a higher atomic number copper or aluminium?

A

Copper - greater photoelectric absorption efficiency.

204
Q

filtration on an xr beam will cause what to the minimum and effective photons?

A

increase

205
Q

do photons have mass

A

no

206
Q

what kind of filter for xr beam is used in mammography?

A

malibdium

207
Q

how do you compensate for having a grid in radiography

A

photons get absorbed so need more mA across filament to produce more electrons and thereefore more photons.

208
Q

what is the cost of having a large air gap?

A

though less noise, also less sharp image.

overcome this by smaller focal spot or bigger focus to object distance.

209
Q

What does the CT number represent?

A

The average linear attenuation coefficient in the voxel

210
Q

what is the HU of white matter?

A

20 - 30

211
Q

Partial volume effect:

thin high contrast object at an oblique angle will show as what

A

it will appear larger.

212
Q

why is the anod cathode parallel to the z axis

A

minimise the anode heel effect

213
Q

what are some features of 4th gen scanners?

A

larger focus to patient distance - means higher dose needed.
Detectors all the way round - more expensive.

214
Q

In CT - detectors should have what properties?

A

fast response, negligible afterglow

wide dynamic range

215
Q

Solid state detectors are worse than ionization chambers for what one thing?

A

they are less sensitive.

but smaller and more stable

216
Q

what are the features of scanograms?

A

minimal scatter but poor resolution

217
Q

Radionuclides

why is it that the material from a cyclotron can easily be seperated?

A

They have different atomic numbers so different physical properites.
Protons are added

218
Q

do isomers have the smae half life

A

no

219
Q

what type of ernegy does beta decay emit?

A

a continuous spectrum - antineutrino and beta split the enregy in different amounts.

220
Q

MRI: when is chemical shift used?

A

fat sat techniques an opposed phase imaging

221
Q

gradient echo in MRI has what type of weighting?

A

T2*

222
Q

MRI: what is the brightness of fat in different PD T1 adnT2

A

bright in PD and T1. Bright in T2 but not as bright as water.

223
Q

what causes a low T2 signal?

A

melanin, calcification, fibrous tissue, high protein content and flow void.

224
Q

phase encoding direction should be in what direction acorss the imaged object

A

the shortest

225
Q

what is the ernst angle?

A

at this anlge get the miximum the magnetic resonance signal for a given tissue T1. (and at a given TR)

226
Q

in MRI what is the acquisition matirx normlly?

A

64 x 64

227
Q

In STIR - what else in addiiotn to fat is supressed?

A

Other tissues with similar T1.
- mucoid tissue, haemorrhage, protein rich fluid, gad
melanin (sometimes)

T1 times Mucoid, haemorrhage, protein, melanin.

228
Q

motion artefacts in MRI occur in what direction?

A

the phase encoding direction

229
Q

SNR i sproportional to what of the bandwith in MRI

A

inversely proportional to the quare root of bandwith

230
Q

which gives a stronger signal spin echo or gradient?

A

spin echo. Gradient angle reduces the signal .

231
Q

what thickness of aluminiium do filters need to be

A

2.5mm

232
Q

At the anode - elastic interactoin happens if kV is less than

A

10eV

233
Q

At the anode - inelastic interactoin happens in what three ways

A

heat

characteristic

brehamstrauling

234
Q

Which of characteristic and brehmstrauling is the most?

A

Bremstrauling is 80%

235
Q

what is meant by beam quality?

A

Ability to penetrate

236
Q

Beam quanitty means what?

A

number of photons

237
Q

What is the angle of deflection in Compton

A

between straight ahead and down to the angle of deflection.

238
Q

Is compton coherant or incoherant?

A

incoherant

239
Q

if high energy of photon to electron - what kind of angle of deflection of photon occurs

A

high angle of deflection

240
Q

What is the compton attenuating coeeficient?

A

Prob of a compton reaction

241
Q

What does compton rely on

A

density of material and electron density.

242
Q

Apart from hydrogen, in every gram of material there are the same number of

A

free electrons

243
Q

Photoelectric interact - what happens to the energy of the photon

A

completely absorbed

244
Q

when does the auger electron get released?

A

Low Z, get complete absorption

245
Q

equation for PE

A

p x Zcubed / energy cubed

246
Q

LAC equation

A

0.693 / HVl

247
Q

what is the atomic number of bone

A

13.8

248
Q

what is the atomic number of soft tissues

A

7.4

249
Q

LAC is combination of

A

PE and compton

250
Q

What is the mass energy absorption coefficient MAC =

A

LAC / density

251
Q

Benefit of MAC

A

removes all density, can compare number which relies more on Z

252
Q

Beam quality equation

A

kVp + HVL

253
Q

how does a wider beam affect scatter? and HVL?

A

higher scatter therefore a misread increased HVL as some of the scatter is registeredas the primary beam.

254
Q

DQE using SNR equation

A

DQUE = ( SNR out / SNR in ) asquared

255
Q

if spatial frequency increases what happens to the MTF

A

decreases

256
Q

contrast equation

A

proprotional to (U1 - U2 ) x thickness

257
Q

what impact does scatter have on image

A

reduces contrast

258
Q

how to overcome scatter

A

large air gap or scatter grid

259
Q

MTF of 1 means

A

range in the image is the same

260
Q

MTF < 1

A

lower range in image

261
Q

MTF = 0

A

No info in image

262
Q

Noise relative to signal equation

A

1 / square root of Number of photons

263
Q

Noise equation

A

square root of number of photons

264
Q

SNR =

A

N / square root of N

also means just square root of Number of photons

265
Q

What are the causes of unsharpness

A

Geometric
image receptor
movement
edge

266
Q

Geometric unsharpenss happens how?

A

penumbra

267
Q

Penumbra is proportional to what

A

XR focal spot size x Distance of object to film / distance from source to object

268
Q

plain film radiography - magnification is what?

A

M = image size / object size = distacne to image from source / distance to object from source

269
Q

what are units of MAC

A

cm squared / kg

270
Q

how can we measure the size of the focal spot?

A

pin hole imaging

271
Q

In fluoroscopy the output screen is what material ?

A

silver activated zinc cadmium sulphide

272
Q

Where are dynodes used?

A

Electron multipliers?

273
Q

Where are focusing electrodes used?

A

II

274
Q

What is brightness gain?

A

ratio of output phosphr brightness to input phosphor brightness

275
Q

What is the readout of CCD in Fluoro?

A

30 f/s

276
Q

What is the normal tube current in fluro?

A

lower than others, 25Kv

277
Q

ABC is picked up wher eon the image?

A

centre of the output screen

278
Q

vignetting causes what?

A

magnification at the edges of the film

279
Q

What happens to SNR after DSA?

A

SNA goes down as noise is added

280
Q

How much is the lag in Image intensifiers?

A

1 ms

281
Q

Which is better in fluoro - flate plate detectors or image intensifiers with regard to quantum efficieny?

A

both the same

282
Q

Why does a grid increase dose in fluoro?

A

less signal so more dose is given to patient to ensure enough brightness

283
Q

Which is smaller a photospot camera or a spot film?

A

photospot is smaller

284
Q

Continous or pulsed gives better resolution in fluoro?

A

pulsed

285
Q

What is the contributer to stray radiation?

A

scatter from the patient

286
Q

Operator at 1m gets how much of the dose?

A

0.1%

287
Q

Beta rays emit energies in WHAT

A

a continous spectrum of energy (due to antineutrino)

288
Q

In US how big are the microbubbles?

A

1 - 10 micrometeres

289
Q

doppler shift equation is what

A

F = 2vF cos0 / c

290
Q

Us what is the equation of MI

A

peak rarefractional pressure / square root of frrequency

291
Q

how can you increase the MI in US

A

lower the frequency or increase the rarefractional pressure.

292
Q

What are the three types of pulsed doppler?

A

Colour
- give a box and direction

Spectral
- sonogram

Power
- good for low flow

293
Q

Why are the edges of a fluro darker?

A

vignetting

  • less focusing of electrons
  • magnified at edges therefore darker image here also
294
Q

what is the Fluro input energy?

A

1 miro Gray / second

295
Q

How much should vignetting be kept below?

A

below 25%

296
Q

in fluro - a single photon at the input causes how many electrons and then how many photons?

A

goes to 3000 electrons

then 100 000 light photons at the output (green)

297
Q

input phospher is made of what in fluro?

A

Caesium idodide

298
Q

in fluro the focus to skin distance is usually

A

less than 45cm

299
Q

With regards to MRI and the coils

- Permanent coil offers what?

A

0.3T

300
Q

Resistive offers what (MRI coil)

A

0.5T

301
Q

What does the faraday cage do in MRI?

A

protects from external magnetic forces

302
Q

What is the maximum T to staff limbs?

A

5T

303
Q

in CT what is the minimum detectable contrast?

A

0.5%

304
Q

Which has a higher CT number contrast or bone?

A

Contrast

305
Q

What decides the size of the voxel?

A

The width of the XR beamm

306
Q

in CT - what happens to quantum noise as you increase the FOV

A

the noise decreases

307
Q

what is CTDI?

A

the amount of radiation hitting the phantom

308
Q

CTDIw

A

accounts for a cylindrical person and beam hardnein.
Middle third
Outside two thirds

309
Q

CTDIvolume

A

CTDIw / pitch

310
Q

Dose legnth product

A

CTDI vol x ????

311
Q

what is the atomic number and K edge of Iodine?

A

Atomic number is 53 and K edge is 33

312
Q

How big is normal focal spot in radiography?

A

1mm

313
Q

How many chambers does an AEC have?

A

3

314
Q

critical angle of refraction in Ultrasound

A

when the refracted beam is parallel to the border

315
Q

Ultrasound intensity and amplitude are proportional how?

A

I prop to amp squared

316
Q

a low kV in film causes scatter to

A

decrease

317
Q

what is the minimum dose needed for XR

A

3 microGray

318
Q

in radiography - low kV vs high kV and their proportions to the output

A

in low kV - output is prop to kV CUBED (mammography)

in high kV - output is prop to kV squared

Physics session (6 decks)

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